The growth and metastasis of most tumors require angiogenesis (the growth of a network of blood vessels for supplying nutrients and oxygen to and removing waste products from the tumor tissue). Therefore, inhibiting tumor angiogenesis becomes a potential way to treat cancer. Capability of imaging tumor angiogenesis is highly desirable for cancer diagnosis and monitoring tumor response to anti-angiogenesis treatment. Recently, molecular imaging of tumor angiogenesis attracts much attention because many proteins and molecules are specifically associated with tumor angiogenesis. Although several imaging modalities (SPECT, PET, MRI, Ultrasound, and Optics) have been reported to successfully image these unique molecules in tumor, no single modality is perfect and sufficient to obtain enough information. Multimodality molecular imaging can offer synergistic advantages over one modality alone and is being actively developed. More importantly, simultaneous multimolecule imaging is highly desirable because (1) currently it still remains unknown whether tumor cells will find alternative routes to vascularize when one mechanism of angiogenesis is blocked due to anti-angiogenesis treatment;(2) it has been found that tumor angiogenesis may be regulated by more than one type of molecules and cross-talk between two types of molecules may exist. Therefore, simultaneous multimolecule imaging is crucial in understanding the mechanisms of tumor angiogenesis and controlling antiangiogenic cancer therapy. Ultrasound and fluorescence optical imaging techniques are two complementary and cost efficient modalities, but each of them suffers from significant problems. In this project, by combining ultrasound and fluorescence optical imaging techniques, a new hybrid imaging modality will be developed: ultrasound-switchable fluorescence imaging based on fluorescence resonance energy transfer (FRET-USFI). FRET-USFI consists of two major components: ultrasound-switchable fluorescence imaging contrast agents and an ultra fast acousto-optical imaging system. FRET-USFI can potentially image multiple molecules simultaneously based on a multicolor fluorescence imaging technique, which is difficult when only ultrasound technique is used. Also, FRET-USFI is expected to have higher molecule sensitivity than the ultrasound technique alone. Lastly, ultrasound molecular imaging modality can be easily incorporated into the FRET-USFI, which enables FRET-USFI to take advantages of the ultrasonic techniques. The specific aims of this project is to develop (1) FRET-USFI imaging contrast agents and (2) an ultra fast acousto-optical imaging system for FRET-USFI, and (3) to demonstrate the feasibility of FRET-USFI in tissue-like phantoms and living animals. PUBLIC HEALTH RELEVANCE: The proposed imaging technique can simultaneously image multiple types of molecules that regulate the formation of new blood vessels in a tumor. If successful, it will be a powerful tool not only for research of understanding tumor development and metastasis, but also for evaluation of tumor treatment efficiency.